snail.go: 檢查是否在圖片上
func (s *Snail) IsOnClick(mouseX, mouseY int) bool {
	return s.PosX <= mouseX && mouseX <= s.PosX+40 && s.PosY <= mouseY && mouseY <= s.PosY+40
}
app.go: 取得滑鼠座標
func (g *App) Update() error {
	mx, my := ebiten.CursorPosition()
	if inpututil.IsMouseButtonJustPressed(ebiten.MouseButton0) {
		if g.snail.IsOnClick(mx, my) {
			g.canPrompt = !g.canPrompt
		}
	}
    // ...略
    
    if g.canPrompt {
        // 執行可以輸入
    }
}